Perfluoro n-alkyl piperidines



Patented Mar. l0, 1953 UNITED STATES PATENT OFFICE 2,631,151 PERFLUORON-ALKYL PIPERIDINES No Drawing. Original application May 12,

Serial No. 161,717.

Divided and this application May 21, 1952, Serial No. 290,316

2 Claims. 1

This application is a division of Ser. No. 161,717, filed on May 12,1950 as a continuation-in-part of our application Ser. No. 29,955, filedon May 28, 1948 (now abandoned).

The present divisional application claims heterocyclic fluorocarbontertiary amines of the fully fluorinated N-alkylpiperidine class.

This invention in its broad aspects relates to our discovery of a newand useful class of fluorinated carbon compounds, namely, the saturatedfluorocarbon tertiary amines. In these novel compounds the moleculescontain only carbon, fluorine and nitrogen atoms and each nitrogen atomis directly bonded to three carbon atoms.

These compounds constitute the family of fully fiuorinated analogues ofthe family of saturated hydrocarbon tertiary amines, the carbonnitrogenskeletal structure being the same but all hydrogen atoms being replacedby fluorine atoms. These compounds are termed fluorocarbon amines merelyas a matter of expediency in order to conform with commonly usednomenclature practice. The tertiary amines of conventional organicchemistry are regarded as derived from ammonia, NHs, by replacement ofthe three hydrogen atoms by three hydrocarbon radicals. The presentcompounds maybe correspondingly regarded as derived from nitrogentrifluoride, NF3, by replacement of the three fluorine atoms by threefluorocarbon radicals.

The present compounds have physical and chemical properties which areentirely different from those of the corresponding hydrocarbon tertiaryamines, as will be indicated in more detail hereafter. They are membersof a disparate class of tertiary amine compounds which is sui generis.

The present family of compounds embraces cyclic as Well as non-cycliccompounds, and polyamines as well as monoamines, all of which have theirstructural analogues in the hydrocarbon system of tertiary amines. It isour discovery that the electrochemical process which we employ is ageneral process capable of producing the fully fluorinated analoguesofall of the saturated hydrocarbon tertiary amines, as distinguished fromspecial processes capable of preparing particular species or types ofcompounds only.

We have found that the compounds of the present class can be directlymade from the corresponding hydrocarbon amine compounds as startingmaterials by employing the novel electrochemical process broadlydescribedv and claimed in the copending application of one of tailhereafter.

Those compounds which contain five or more carbon atoms in the moleculehave boiling points above room temperature and hence are normallynon-gaseous. Compounds containing eight or more carbon atoms haveboiling points near to or above that of water and may be referred to ashigh-boiling compounds.

These fluorocarbon tertiary amine compounds are water-insoluble; theyhave a high degree of chemical inertness; they are non-flammable; andthey can be heated to moderately elevated temperatures in Pyrexlaboratory type glassware without reacting or decomposing. They do notreact with metallic sodiumor potassium at room temperatures. Makingcomparisons with nonfluorine compounds on the basis of molecularweights, these new compounds have exceptionally low boiling points, lowrefractive indices, low viscosities and low surface tensions. They arecolorless and are apparently odorless when in pure form.

These compounds have properties which permit of use for many of thepurposes for which saturated fluorocarbons can be used. They can beemployed as refrigerants, inert diluents for chemical reactions,solvents, hydraulic mechanism fluids, heat transfer media, turbineimpellants, transformer liquids, dielectrics, and lubricants. They canalso be used as intermediates in the manufacture of other compounds.

Various illustrative sub-classes of our novel compounds will now beindicated and exemplary compounds Will be mentioned, following which anumber of experimental examples will be set forth to illustrate thegeneral utility of the process and to provide detailed data on variousof the compounds. v

The saturated aliphatic trifluorocarbon monoamines (containing a singlenitrogen atom) are derivable from the corresponding trialkyl amines, andhave the same structureexcept that the hydrogen atoms have beenentirely. replaced by fluorine atoms. The nitrogen atom of the moleculeis directly bonded to'each of three saturated aliphatic fluorocarbongroups. These compounds have the formula:

RIRHRIHN I are normal straight chains.

C'Fs

CFa-N The following table shows how the boiling points of thesecompounds vary with the number of carbon atoms, and has been simplifiedby including only the normal (straight chain) compound wherein the threefluorocarbon groups are the same. Boiling points at 760 mm. pressure aregiven. These listed compounds are all fluid (gaseous or liquid) at roomtemperature.

Gompounds B P. (G)

(CF3)3N 1 ll (CzFsh 70 (C3F7)3N 130 (C4F9)3N 178 (CsFulsN 218 (CsF1s)sN258 (C1F 5)3N 294 a i1)3N It will be noted that these boiling points aresubstantially lower than those of the corresponding compounds of thehydrocarbon trialkyl amine series (despite the fact that the molecularweights are much higher). Thus the B. P. of (CzFshN is 70 C. as comparedwith 89 C. for (C2Hs)3N. The B. P. of (certain is 258 C. as comparedwith 300 C. for (CeH13)3N.

The boiling points of these compounds are higher than those of thesaturated aliphatic fluorocarbons having the same number of carbonatoms, as is illustrated by the fact that the B. P. of normal CsFm isabout 55 C. as compared to 70 C. for (CzFs)aN.

Unsymmetrical as well as symmetrical compounds are included. The lack ofsymmetry may arise from diflerent numbers of carbon atoms in thefluorocarbon groups, as in the case of (CF3)2N(C5F11). Another type ofnon-symmetry exists when the groups difler as to branching, as when onegroup is branched and the others Both types of non symmetry may bepresent, as in the case of (CFs) 2 N(iSO-CsFn) Unlike the trialkylamines, even the lowest trifluorocarbon amines are not onlywater-insoluble but do not react with, and are not soluble in, themineral acids. They are not miscible with the trialkyl amines. Theyseparate out when mixed with liquid hydrogen fluoride, although thetrialkyl amines are highly soluble in the latter.

Tests made both at room temperature and at the temperature of boilingwater (100 C.) indicate that these compounds do not react with any ofthe following: concentrated l-ICl, concentrated H2804, concentratedNaOl-I, 30% H202, HNOz, and methyl iodide.

The invention is not limited to the aliphatic series of compounds. Thenitrogen-bonded saturated carbon-chain groups need not be of theopen-chain type; since one, two or all three may be alicyclic,containing a saturated fluorocarbon ring (closed chain). Examples ofsuch compounds are (CeF11CF2)3N, corresponding totricyclohexylmethylamine; (CsF11CF2CF2)3N, corresponding totricyclohexylethylamine;

(CFs) zNCeFn corresponding to dimethylcyclohexylamine;

(CsFn) zNCFs corresponding to dicyclohexylmethylamine; and (CsF11)sN,corresponding to tricyclohexylamine.

The nitrogen atom can be in a ring (which may be regarded as formed bythe closure of two nitrogen-bonded fluorocarbon chains), as illustratedby the fully fluorinated N-allrylpiperidines claimed in the presentapplication, such as C'sFmNCFa, corresponding to N-methylpiperidine, andCsFmNCzFs, corresponding to N-ethylpiperidine, etc., wherein CsFmN is afluoropiperidine group. A further illustration is CsFmNCeFn,corresponding to N-cyclohexylpiperidine. The previously mentionedelectrochemical process is adapted to the production of such cycliccompounds from the corresponding hydrocarbon amine compounds, thehydrogen atoms being replaced by fluorine atoms.

The electrochemical process produces as byproducts various fragmentationproducts containing fewer carbon atoms than the parent compound, due tocleavage of carbon-nitrogen and even carbon-carbon bonds in the case ofsome molecules.

Another type of by-product consists of fluorocarbon tertiary aminecompounds which contain a greater number of carbon atoms and which havehigher boiling points than the fluorocarbon tertiary amine whichcorresponds to the starting compound. These are presumably formed by thecombining of free radicals in the electrolyte solution. Thesehigh-boilers range from freeflowing liquid up through viscous oilyliquids, greases, tacky solids, and brittle resinous solids.

Electrochemical method of making As previously stated, the compounds ofthis invention can be conveniently made by electrolyzing solutions ofthe corresponding hydrocarbon amine compounds in liquid hydrogenfluoride, the end result of which is to replace hydrogen atoms withfluorine atoms. The formation of by-products has been discussed above.It is not essential to use a hydrocarbon amine (containing only hydrogenatoms to be replaced by fluorine atoms) as equivalent tertiary aminescan be employed which contain one or more other carbon-bonded atoms orgroups which are replaceable by fluorine atoms in the operation of theprocess. Thus an amine having one or more carbon-bonded hydroxyl groups(OH) can be used, as illustrated by triethanolamine, in which case thehydroxyl groups as well as the carbon-bonded hydrogen atoms will bereplaced by fluorine atoms. Unsaturated and aromatic amine startingcompounds can be employed, which have the same carbon-nitrogen skeletontructures as the desired saturated end products, saturation resultingfrom fluorine addition in the operation of the process.

A simple type of electrolytic cell can be used. employing a nickel anodeand an iron or steel cathode, for example. An iron or steel containercan be used, which may be employed as a cathode, with a cover of iron orsteel which is bolted in place. Anode and cathode plates, incloselyspaced alternating array, can be suspended from the cover. Asuitable gasket material, and insulating material for electrodemountings and leads, is Teflon (polytetrafluoroethylene). An upperoutlet for gaseou products, an upper inlet for charging materials, and abottom outlet for liq products, may be provided. The cell may beprovided with a cooling jacket for maintaining a desired operatingtemperature.

Commercial anhydrous liquid hydrogen fluoride can be used. This normallycontains a trace o water, but water need not be present and highlyanhydrous hydrogen fluoride can be used. Additional water can bepresent, but more than a few percent will seriously reduce the operatingefficiency. The amine starting compounds are soluble in this material.

A cell potential of about 4 to 8 volts D. C. ha been found suitable. Acurrent density of about amperes per square foot of anode surface can beobtained. Voltages suificiently high to result in the formation of freefluorine are avoided. The process does not depend upon the generation offree fluorine and the latter, if produced, would result in explosions,electrode corrosion, and undesirable reactions.

The preferred operating pressure is atmospheric pressure or a moderatelyelevated pressure, and the preferred operating temperature range isabout 0 to 20 C.; but higher and lower operating pressures andtemperatures can be employed.

Liquid fluorinated amine product compounds separate as a constituent ofa liquid which is immiscible with the electrolyte and settles to thebottom of the cell from which it can be withdrawn. The latter can bewashed with a base and with dilute sulfuric acid, and fractionallydistilled to yield the desired fully fiuorinated amine product. Thedesired fully fluorinated amine product can be further purified byrefluxing with NaOH solution for a period of several hours. Thiseffectively eliminates any hydrogen-containing byproduct contaminants.

Example 40 grams of N-methylpiperidine was dissolved in 2000 grams ofcommercial anhydrous liquid hydrogen fluoride and electrolyzed in themanner Boiling point (at 730 mm.) 65.0-65.5 C. Refractive index (at 24C.) 1.275 Density (grams/cc. at 24 C.) 1.760 Molecular weight (found)336 Molecular weight (02.10.) 333 This compound has the followingstructural formula:

Having described various embodiments of the invention, for purposes ofillustration rather than limitation, what we claim is as follows:

1. Saturated fluorocarbon tertiary monoamines of the fully fiuorinatedN-alkylpiperidine class, having the formula:

where R represents a saturated aliphatic fluorocarbon gnoup.

2. The new and useful compound N-trifluoromethyldeoafiuoropiperidine,having the formula: C5F10NCF3.

EDWARD A. KAUCK, JOSEPH H. SIMONS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Simons Dec. 6, 1949 Number

1. SATURATED FLUOROCARBON TERTIARY MONOAMINES OF THE FULLY FLUORINATEDN-ALKYLPIPERIDINE CLASS, HAVING THE FORMULA: